An electronic device can receive power from a wireless power transmitter. In one example, a power transmitter circulates a varying current through an electromagnetic coil to induce a voltage across the terminals of a magnetically coupled corresponding coil within an electronic device, thereby inducing a current useful to the electronic device inversely proportional to the impedance of the device at that time. In a typical example, the electronic device directs the induced current to a circuit configured to recharge a battery or power a load.
Some conventional electronic devices send data back to the power transmitter by selectively changing their effective impedance; changes in the operating point are monitored by the wireless power transmitter to recover the data. However, the rate at which data can be sent in this manner is low.